The perennial challenge for the industry is to make parts, assemblies and machinery lighter and more efficient. This has led to progressively wider application of composites due to their excellent strength, stiffness and corrosion resistance properties. Composite components are assembled predominantly by fastening, which makes drilling a common machining process for such components. Delamination of the component surface at entry and exit of the drill is a drilling defect frequently encountered. Assessment of the severity of the delamination is necessary for correction and improvement of the performance of the parts and assemblies. Over a period of time, several factors have been suggested as the index of delamination for comparison and control. Also, various techniques are being adopted to measure the extent and severity of delamination so as to calculate the assessment factor. This study aims to present and review the different means and methods for the assessment of delamination.

No abstract

The main objective of this study was to produce aligned hemp fibre mats from high strength hemp fibres using dynamic sheet forming (DSF). Alkali treatment of hemp fibre was carried out at ambient and high temperature to separate fibres. Single fibre tensile testing was used to assess the tensile properties of the fibres. It was found that the highest tensile properties were exhibited by high temperature treated fibre, whereas the tensile properties exhibited by ambient temperature treated fibre were lower than for untreated fibre. It was also found that fibre granulated after high temperature treatment, was better separated than that granulated before high temperature treatment. This well-separated fibre could successfully be formed into mats using DSF. The orientation of the formed mat was analysed using ImageJ (NIH, USA) software by which the potential of DSF to produce aligned hemp fibre mat was supported. The mechanical performance of composite reinforced by these aligned hemp fibre mats were assessed.

The benefit of using alkali-treated hemp fibre as the reinforcement for rotationally moulded polyethylene composites was evaluated in this research. Untreated and alkali-treated hemp fibre were characterised using different techniques such as scanning electron microscopy (SEM), thermal analysis, and Fourier transform infrared spectroscopy (FT-IR). These techniques showed that the alkali treatment removed non-cellulosic components from hemp fibres, which improved their separation and thermal resistance. Composites with alkali-treated fibre resisted the exposure to elevated temperatures for prolonged periods (characteristic of the rotational moulding process) with no apparent signs of thermal degradation, unlike when untreated fibre was used. The effect of using maleic anhydride grafted polyethylene (MAPE) as a coupling agent was also investigated. The addition of 3 wt% MAPE improved the properties tensile strength and Young's modulus of composites with treated hemp fibre, which was attributed to better fibre-matrix adhesion. Different fibre contents were assessed in this research to produce rotationally moulded composites; a poor fibre distribution was observed above 5 wt% fibre content, which resulted in low tensile strength and Young's modulus.

Orientation of fibre preforms is an important factor that affects the properties of short natural plant fibre composites. In this paper, oriented short hemp fibre mats were produced using dynamic sheet forming and the fibre orientation distribution in the mats was analysed using ImageJ software as well as by a simple program developed on a MATLAB software package. The OrientationJ plug-in of ImageJ gave an orientation distribution curve with a peak at a predominant direction of 0° supporting alignment during dynamic sheet forming and from MATLAB software, a mean ratio of 0.64 was obtained for the oriented mats compared to 0.74 for an aligned bundles.